Toxocara canis (more common) or Toxocara cati, respectively, parasites whose primary host is the dog or cat, can infect individuals residing in Mississippi. Clinicians should consider these diagnoses when compatible exposures or clinical manifestations are present.

1. Toxocara infection is highly prevalent worldwide and in Mississippi. In the United States, 5% of the population ≥6 years old are Toxocara seropositive, with rates in Mississippi nearly twice the national average.^1–3

2. Contact with soil in areas in which dogs or cats have defecated - including playgrounds and sandboxes - puts you at risk for infection. Children and adolescents may be at risk due to behavior such as exposure outdoors with play. More rarely, infection can occur by eating undercooked meat of an infected animal (e.g., rabbit, chicken, or lamb) (Table 1).^4–6

3. Clinical illness can manifest as abdominal pain, seizures, palpitations, or vision problems. When a person ingests eggs from a contaminated environmental source such as soil or the hair of a pet, the larvae within the eggs hatch in the intestine and then migrate to the organs, including the liver, brain, eyes, heart, and skeletal muscle. Since humans are a dead-end host, the parasite will die in these tissues, causing inflammation. Granuloma formation or evidence thereof may be seen on imaging, ocular exam, or on tissue biopsy.^1,2,4,5,7,8

4. Clinical and laboratory features of covert toxocariasis or visceral larva migrans may not be obvious. In visceral larva migrans (VLM), in which the liver, lungs, or more rarely the heart and kidneys are affected) and covert toxocariasis, patients may present with incidental eosinophilia without symptoms, or with fever, hepatomegaly, or lung findings, depending on the stage of migration. Pulmonary symptoms (notably wheezing and rhonchi), signs of myocarditis, or urticaria may be present. The true incidence of disease is not known as many people are infected or exposed to Toxocara and do not develop overt symptoms.^2,4,8–11

5. Neurological and ocular manifestations can also occur, and require consideration of treatment with anti-helminthic therapy, and possibly steroids. In neural larva migrans (NLM), children have central nervous system invasion which may present clinically in the form of either seizures or encephalopathy as or consequent to larvae migrating through the brain. In cases of ocular larva migrans (OLM), resultant retinal pathology may lead to visual changes, strabismus, retinal detachment, uveitis, endophthalmitis, or granulomas (the latter which may not be seen on imaging or ocular examination directly; see Figure 1).^2,4,8–11

6. Diagnosis of toxocariasis cannot be made by checking the stool for ova and parasites. Because Toxocara larvae are unable to complete their life cycle in humans to develop into adult worms releasing eggs in the intestine, a patient’s stool examination will not reveal infections. Rather, assessment of clinical features with serologic tests makes the diagnosis. Animals (dogs/cats) may expel visible worms from their intestine but the eggs themselves are the infective form and require 2-4 weeks to mature in the soil. Positive serology, combined with consistent clinical signs and symptoms, are required for a diagnosis of toxocariasis. Serological screening tests from commercially available labs and confirmatory testing through CDC are available. Case discussion may be undertaken with an infectious disease specialist or with CDC as to whether confirmatory testing may be indicated.^4,5,12,13

7. Diagnosis and management of OLM should be undertaken with an ophthalmologist with specific expertise in Toxocara management. Sensitivity for OLM is lower using sero-diagnostic assays, and thus an ophthalmologist with experience is essential in making diagnosis. The benefit of specific anthelmintic therapy for treating OLM has not been established, particularly given the exacerbation of host inflammation that could result. Ophthalmologists may recommend steroids topically or systemically to reduce intraocular inflammation.^2,4,5,8,11

8. Antihelminhic drugs against toxocariasis are safe and readily available. Treatment of choice for VLM is albendazole for 5 days although longer courses may be used in more complicated infections (e.g. heart, central nervous system). Positive serology itself does not necessitate treatment. An alternative treatment for toxocariasis is mebendazole, although albendazole is preferred particularly in OLM and neural larva migrans because of the lack of blood brain barrier penetration and suboptimal gastrointestinal absorption.^2,4,5,14,15

9. Strongyloides should be screened for using a serological antibody test, for which there are commercially available versions. Testing is also available at CDC. This should be done even in patients without travel history if steroids are being considered for toxocariasis. Because of the risk of Strongyloides hyperinfection syndrome, this infection should be screened for and considered before initiating corticosteroid therapy.^4,5,15

10. Washing your hands after contact with soil or with the fur of animals on which there may be traces of feces (or even the paws of a dog!) is essential to decrease chances of infection. Reinfection can occur with repeat exposure. Sandboxes and other play areas where dogs and cats could defecate should be covered and avoided completely if waste is visible. Appropriate disposal of dog and cat feces and routine and frequent deworming of dogs and cats are essential. Food should be thoroughly cooked as infection from undercooked meat, although rare, can occur (Table 1).^4,15

Figure 1.Image of Toxocara egg, detected in the feces of a shelter dog (Jackson, Mississippi).

Eggs are deposited in the soil and require 2-4 weeks to mature and become infective. Larvae within the eggs hatch once ingested in the human intestine. (Figure Courtesy of Richard S. Bradbury PhD, Federation University, Australia).